MDF still viable?

The early Mendel 90 was built with MDF 12mm iirc, the new ones use composite ali Dibond. (I assume the middle ones used some sort of acrylic??

Anyway, dibond seems really expensive, MDF 12 or even 9mm is cheap by comparison. Acrylic sheets not too keen on.

Is there anything I'd need to change dramatically if I followed the plans for the current Mendel 90 and used MDF 12mm?

Would 9mm be sufficiently rigid (I think I've got a couple of sheets in the garage)?

I'm still deciding what to do for the next printer, so apologies for all the slightly random questions.

Hi,

I have made my custom "Sturdy" with MDF. I have been using the printer for six months and the MDF is all good.
However you do have to treat the MDF with primer and then paint it with 2 layers to prevent MDF from drying out.

I have 12 mm so I can't tell if 9mm will be strong enough.
It also depends on te size rods you are going to use.

There are rod options?
For the m mdf I know all about painting, it's a dark art to get a good, durable finish what is interesting is that once I start factoring in paint, the composite might be a similar price.

You are right about that. The price for the painting and primer was an unpleasant surprise one after I obtained my MDF cheap. (14 euro)
I paid around 44 euro for primer, paint and a brush.

I'm using 12mm smooth rods for the Y-axis and 8mm for the X and Z axis.
The current dibond Mendel90 uses 6mm rods so that would maybe best for your 9mm MDF you are using.

It's amazing you can actually get a mirror like finish on MDF, but the work involved is ... involved.

6mm rods seem awfully flimsy, now I've got some lengths of 8mm I was considering 12mm myself.

I am in the process of building a "Sturdy", but since I live in the USA I am using 1/2" (12.7mm) MDF. I am using gloss black Minwax "Polyshades", which is a polyurethane varnish and stain all in one (the lady at the paint counter at Home Depot recommended the Minwax oil-based polyurethanes for sealing MDF). Just put the second coat on one side of each piece and all the edges. The first coat ended up looking dark grey, with lighter edges (the edges soak up the finish like a sponge). The second coat is quite a bit darker. I will be coating the other side of the parts (and the edges, again) tomorrow. Might even do a third coat (and a fourth on the edges, if necessary) after that coat dries, just to be safe. I am using the standard 8mm threaded/10mm smooth rods specified for the "Sturdy".

The dibond kit uses 8mm smooth rods, not 6mm.

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[www.hydraraptor.blogspot.com]

Quote
UkIan
It's amazing you can actually get a mirror like finish on MDF, but the work involved is ... involved.

Which is why I'm not going for a perfect finish, as far as looks go. Sealed, and functional, is my goal...

Edited 1 time(s). Last edit at 10/07/2014 04:08AM by Rich K..

Totally agree

I suspect that the diameter of the smooth rods is a far more significant factor than the finish on the mdf.
If one has an extremely tight budget then I would think that the cheapest way to go would be to look in second hand furniture shops for some sort of table or cabinet made of solid wood that has had a few years to dry out.
One could also take a cheap mdf frame and stabilize it with cheap M8 threaded rods.
The Z axis threaded rods on the Mendel90 are 6mm but the smooth rods, which give the stability, are 8mm.

Quote
Ralph.Hilton
The Z axis threaded rods on the Mendel90 are 6mm but the smooth rods, which give the stability, are 8mm.

In the "sturdy" version, made of 12mm MDF, the Z-axis threaded rods are 8mm and the smooth rods (except for the short piece that goes through the bearing in the extruder) are 10mm - hence, "sturdy".

Good to know, thanks. The 90 seems like the best of the cartesian designs, although I also like the reprap pro mendel design. I think the 90 wins slightly just by having a horizontal X carriage.

I think the RRP Mendel also has a horizontal X carriage. The main difference is you have to tweak a triangular frame to get all the axes orthogonal.

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[www.hydraraptor.blogspot.com]

I think all the RRP ones are vertical, I did have a look on their site. I'm a big fan of their Mendel btw, especially the tri-colour. I actually like the idea of using adjustable rods to align the frame. It gives me wiggle room that I don't have if I have to cut things at right angles (or at the right angles).

I stand corrected it is vertical. I think early versions were horizontal.

The idea of Mendel90 is that you can buy sheet materials cut to size with perfect right angles. In the UK I can buy MDF at a big DIY chain and they cut it for free. For Dibond and Acrylic I can buy it cut to size and with radiused corners on-line. I made prototypes in all these materials buying the sheets ready cut and drilling them myself before I started selling the kits with CNC cut and drilled Dibond.

The other advantage over triangular frames is it is rigid in the directions it needs to be whereas the triangular prism is only rigid in a direction that is irrelevant to the motion.

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[www.hydraraptor.blogspot.com]

I think you're preaching to the converted now. I've just received my a3 sized dibond sheets I bought to have a play with. It's different to what I was expecting, I was expecting a corregated filler, or something like a model airoplane wing which is uber solid until you poke a little hole in it. It feels quite nice I have to say, although heavier than I expected.

B&Q near me do cutting, so I'm still thinking in terms of MDF. I might just crack and do a Mendel90 as per the plans as I've been stealing bits of your design for whatever the hell it is I'm designing/planning anyway.

I did email a local timberyard who advertised cutting, but they didn't bother to reply, so stuff em. I did try to shop local